ECN publication
The dark decay of HONO in reaction-chambers
Published by: Publication date:
ECN 1996
ECN report number: Document type:
ECN-RX--96-039 Other
Number of pages: Full text:
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The decay of gaseous nitrous acid (HONO) was studied in reaction chambersof glass and polyethylene at concentrations in air ranging from 100 ppbv to 10 ppmv and relative humidities between 50% and 80%. The initial decay was independent of the relative humidity and could be described by a second-order process with a rate constant of 8 (-.5) * 10"-"5 ppm"-"1.min"-"1. Only a small amount of NO was formed, showing that the initial decay of HONO is (heterogeneous) removal at the reactor wall. At longer residence times decomposition of HONO into the nitrogen oxide gases was the dominant process and equilibrium between HONO, NO, NO2 and H2O was established. The initial heterogeneous decay was not measurably different in the two types of chambers with their different wall surface materials. When the walls of the chambers had been wet before experiments, the decay was up to ten times more rapid, showing the importance of adsorbed water. Additional surface in the form of copper oxide aerosols or NaCl droplets, present at concentrations far exceeding ambient values, did not accelerate the decay. Whereas the rate of decay was not measurably modified by the NaCl, HONO reacted with the droplets by substituting of the order of 2.5% of the chloride by nitrate. This reaction occurred when the aerosol was present as stable droplets at 80% and as metastable droplets at 50% relative humidity. The extent of the reaction seemed independent of the HONO concentration. A measurable reaction was absent with dry NaCl aerosol at 30% RH. 3 figs., 13 refs.

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